16 März 2015

Bio-based chemicals: Automotive materials go green

Specifying sustainably derived materials – such as new types of rubber and plastic – can help the car industry shrink its carbon footprint

The automotive industry is under huge pressure to go green. Fuel efficiency must rise, while pollution and carbon footprint must fall. Designers and engineers are devising many ways to do this: lighter, more aerodynamic car bodies; tyres with lower rolling resistance; and new ways of sourcing materials.

The new Jaguar F-Type contains bio-materials to reduce carbon footprint Copyright: Rex Features

New materials will be at the heart of the super-efficient car of the future. But as well as cutting emissions by allowing lighter cars, these materials will also boast lower carbon footprints. Almost every part of the car – from body panels and tyres to seat fillings and under-bonnet components – could one day be made from bio-derived materials. And some already are.

Sustainably-sourced car parts are not new. In 1941, with automotive mass production booming in the US, Henry Ford unveiled a plastic-bodied car. It is often referred to as the “Soybean” car, because this was one of the raw materials used in the panels. Their exact formulation is lost to history, but one of the car’s originators said they were made of “soybean fibre in a phenolic resin, with formaldehyde used in the impregnation”.

The thinking behind it was to “conserve steel and boost sales of farm products”, but the project foundered when the US joined the war that year.

But fast-forward nearly 75 years and bio-derived materials are making inroads into the modern car. As with many new technologies, they start at the top. So these new concepts tend to be found in top of the range cars – from Jaguar, Land Rover, Porsche and Subaru.

The new Jaguar F-Type is a case in point. While everything on show is made from traditional materials, one hidden element – the load floor – is made using bio-derived materials. The load floor sits on top of the spare wheel in the boot. The part would typically be made from a glass-filled poly-urethane, but this part is a bioplastic reinforced with flax fibres.

“The plastic is made from food waste like corn cobs and nut shells,” says Tim Sweatman, technical director of UK-based EcoTechnilin, which developed the panel.

Flax delivers parformance

The fibres are effectively a waste product from flax production because they are too short (at 60-80mm) for the textile industry. While the price of textile fibre is around €3.80/kg, these “technical” fibres cost around a fifth of that.

Relying on natural products may seem risky. The weather might wipe out production instantly, while the automotive industry is very conservative and takes to new products very cautiously. “The industry never wants to talk about the ‘green’ aspects of the material, only its performance,” he says.

But, as well as its green advantages – the product is 100% bio-derived, so helps with end-of-life issues – the natural fibres are less dense than glass, so can deliver an instant advantage to car designers. “Customers get very interested the moment they pick up a panel and feel how light it is,” says Sweatman.

In addition to the Jaguar part, Sweatman is hopeful that sister company Land Rover might also start using the material, for applications such as headliners, under-bonnet parts and door trims.

In similar fashion, design consultancy PES Performance has designed a number of bio-derived parts under the UK-funded Elcomap project – which aims to make car body panels from bio-based composites.

It has created rear panels for a Porsche and a front end for a Subaru using a surprising new material: an epoxy resin in which 30% has been replaced by cashew nut oil – which has become more popular as a precursor for making “green” resins. Again, the reinforcement is flax fibre.

“We’ve spent more than 10 years taking weight out of road-going Porsches,” says Dan Fleetcroft, engineering design director at PES Performance. “This gave us a good platform to benchmark what we had done in the past.”

Although the panels showed comparable performance to conventional glass-filled equivalents, Fleetcroft says they were harder to “wet”. However, as volumes increase, he is confident that they will be able to improve the impregnation of the fabrics.

The Porsche parts were a rear bonnet and boot. The boot lid was designed as an upper and lower skin, which allowed the geometry to be moulded and removed from the tooling. Overall, the part was 6kg lighter than the 1mm thick steel original. The thickness of the part ensured a higher stiffness.

Because the component is based on epoxy it was cured in an autoclave, at 120˚C for two hours. Fleetcroft says this is near the limit of what flax fibres can withstand: if the team had been using a phenolic resin, the flax could probably not have taken the higher curing temperature.

Flowers for your car tyres

The Russian dandelion is being engineered for tyre production Copyright: Fraunhofer IME

Many natural resources are concentrated in particular regions of the world: rare earth metals are largely mined in China, for example, while natural rubber production is largely confined to Southeast Asia – where 90% of rubber trees are grown.

The vast majority of natural rubber is used in car tyres. No surprise, then, that regions like Europe and North America are looking for ways to reduce their reliance on imports and find sources of their own. One surprising potential source of natural rubber – and the subject of a number of research projects – is the Russian dandelion.

In this case, the industry is not doing this in order to shrink its carbon footprint – but to reduce its reliance on an imported resource.

One pan-European project, Drive4EU, is looking at the feasibility of using the Russian dandelion as a precursor for natural rubber production. To do this, it will use many techniques that are alien to the automotive industry, such as genetic engineering and improved cultivation and harvesting of crops.

The eight industrial partners and five research organisations intend to breed a plant that is more productive, and design a biorefinery process to harvest the natural rubber within the dandelion. The project began in early 2014, and will last until 2018.

But it is not the first. Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) in Germany – in collaboration with tyre manufacturer Continental – is already building a pilot system in Münster to extract large quantities of dandelion rubber. This is an important step on the path to rubber procurement in Europe, say the researchers.

“Through modern cultivation methods and optimisation of systems technology, we have succeeded in manufacturing high-grade natural rubber from dandelions – in the laboratory,” says Rainer Fischer, head of the IME in Aachen. “The time is right to move this from pilot project to industrial scale. With Continental, we now want to create tyres that are ready for production.”

Using genetic manipulation, the researchers intend to breed plants with a higher rubber content. This, combined with the fact that the crop is less affected by the weather than rubber trees, should lead to more stable production.

The researchers expect to test prototype tyres – made with blends from dandelion rubber – in the next few years. They says they have already proved that the dandelion rubber is of the same quality as that from the rubber tree.

Mastering this whole process is expected to take five years, after which time Continental expects to be making “dandelion tyres”.

“We are investing in this because we are certain it can help us improve tyre production over the long term,” says Nikolai Setzer, the Continental managing director responsible for the tyres division.

Rubber replacement in racing

For many years, Evonik has supplied materials for components on the Lotus Exige – which are then tested under motor racing conditions. Now, Lotus has used a multi-layer tube system that incorporates a bio-based Evonik resin for the first time.

The company has supplied grades of its Vestamid polyamide to Lotus before, for use in its multi-layer line for charge-air cooling. Now, the line incorporates new Vestamid Terra, which is derived from sustainable sources.

The multi-layer tubes are lightweight replacements for rubber hoses and reinforced lines. The MLT 8000 multi-layer tubing system has been used in vehicles worldwide. The current car uses MLT 8000.3 with an orange outer layer. This system is around 870g lighter than cooling line systems with steelflex tubes, a weight reduction of more than 70%.

The coolant lines have three layers: the inner layer is a specially adapted grade of polypropylene; the second is an adhesion promoter layer; and the outer layer consists of the Vestamid (or bio-based Vestamid Terra).

Evonik’s bio-based polyamides have been used commercially since 2010 as mono-layer tubes in air brake lines of utility vehicles, and other applications, but this is the first time they have been used in multi-layer tubing systems for coolant lines.

These are just some of the current applications, though many more will be around the corner: DuPont is developing bio-isoprene – which Goodyear plans to polymerise in order to make tyres; several major suppliers are using carbon dioxide to make polyurethane – a key automotive plastic; and, like Evonik’s Vestamid, an increasing number of bio-based polyamides now exist, which are as robust as their petroleum-derived counterparts.

But beware of the downside. One car owner in South London is convinced that squirrels chewed through his Toyota Aygo because of its bioplastic panels. You have been warned!